Automatic determination and selection of filtering in a cardiac rhythm management device

ABSTRACT

Methods and/or device facilitating and selecting among multiple modes of filtering a cardiac electrical signal, in which one filtering mode includes additional high pass filtering of low frequency signals, relative to the other filtering mode. The selection filtering modes may include comparing sensed signal amplitude to one or more thresholds, using the multiple modes of filtering. In another example, an additional high pass filter is enabled, over and above a default or baseline filtering mode, and the detected cardiac signal is monitored for indications of possible undersensing, and/or for drops in amplitude toward a threshold, and the additional high pass filter may be disabled upon finding of possible undersensing or drop in signal amplitude.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of and priority to U.S.Provisional Patent Application Ser. No. 62/262,043, filed on Dec. 2,2015, and titled AUTOMATIC DETERMINATION AND SELECTION OF FILTERING IN ACARDIAC RHYTHM MANAGEMENT DEVICE, the disclosure of which isincorporated herein by reference.

BACKGROUND

A number of cardiac rhythm management products are available for the usein diagnosis and treatment of various conditions. These may include, forexample, subcutaneous, transvenous, or intracardiac therapy devices suchas pacemakers, defibrillators and resynchronization devices.Implantable, external and/or wearable cardiac monitors are alsoavailable. External or wearable therapy products may includedefibrillator vests and external pacemakers, as well as automaticexternal defibrillators.

FIG. 1, which is taken from Ellenbogen, et al. in CLINICAL CARDAICPACING AND DEFIBRILLATION, 2nd Ed. (W.B. Saunders Co. 2000), at 201,shows the frequency of raw cardiac signals and non-cardiacmyopotentials. The signals include T-waves, which represent ventricularrepolarization and have a frequency content in the range of about 3-9 Hzor so. R-waves are also indicated and represent ventriculardepolarization; the R-wave frequency range is typically from about 20 Hzto about 40 Hz. P-waves, representing atrial depolarization, are stillhigher frequency, in the range of about 30-70 Hz. Myopotentials,representing non-cardiac muscle activity, tend to have frequency contentof 90 Hz and above.

T-wave filtering may be desirable for systems subject to a risk ofT-wave overdetection, which can lead to overcounting of cardiac cyclesand possibly to inappropriate therapy. While filtering the T-wave outmay reduce potential overdetection and inappropriate therapy, it is alsonecessary to ensure that filtering directed at the T-waves does not leadto undersensing of tachyarrhythmias such as ventricular fibrillation orpolymorphic ventricular tachycardia. Such arrhythmias are often detectedby monitoring for and counting the R-waves.

The concern arises because the signals for T and R waves are so closetogether in the frequency domain. For example, a first order high passfilter with a corner frequency at 10 Hz, which would attenuate the 3-9Hz T-wave, will also attenuate a signal at 15 Hz by ten to twentypercent, or more, which can be significant. Given that barely a decade(a tenfold increase in frequency) separates the noted signals, theeffect of a filter directed at one set of signals on other signalsshould be monitored.

New and alternative approaches to filtering control are desired.

OVERVIEW

The present inventors have recognized, among other things, that aproblem to be solved is that of attenuating T-waves while monitoringdetected signals in a cardiac rhythm management system to ensure thatundersensing of R-waves and/or arrhythmias is avoided. To this end, oneexample provides a method or device facilitating and selecting amongmultiple modes of filtering, with one mode including additional highpass filtering of low frequency signals relative to the other filteringmode. In an example, over-attenuation of desirable cardiac signal suchas the R-wave is avoided by comparing the detected signal amplitude toone or more thresholds, using multiple modes of filtering. In anexample, an additional high pass filter is enabled, over and above adefault or baseline filtering mode, and the detected cardiac signal ismonitored for indications of possible undersensing, and/or for drops inamplitude toward a threshold, and the additional high pass filter may bedisabled upon finding of possible undersensing or drop in signalamplitude.

This overview is intended to briefly introduce the subject matter of thepresent patent application, and is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 shows the frequency content of certain biological signals;

FIG. 2 shows an illustrative implantable medical device system;

FIG. 3 provides a highly schematic depiction of an illustrative cardiacrhythm management device;

FIGS. 4-7 illustrate various methods in block flow form; and

FIG. 8 provides another depiction of an illustrative cardiac rhythmmanagement with functional blocks and data flow connections shown.

DETAILED DESCRIPTION

FIG. 2 shows the S-ICD System™ from Cameron Health, Inc., and BostonScientific Corporation, as implanted in a patient. The system isimplanted in a patient 10 with a canister 12 in the left axilla at aboutthe level of the cardiac apex. A lead 14 is placed subcutaneously,beneath the skin and over the ribcage of the patient, with a firstportion extending along the inframammary crease to the xiphoid, and thensuperiorly parallel to and about 1-2 cm to the left of the sternum. Aproximal sense electrode 16, shocking coil electrode 18, and distal tipsense electrode 20 are provided along the parasternal portion of thelead 14. The entire system is implanted outside of the ribcage.

The canister 12 may include componentry appropriate for communication(such as RF communication, inductive telemetry or other suitablecommunication linkage) with an external device such as a programmer 22.For example, during an implantation procedure, once the canister 12 andlead 14 are placed, the programmer 22 may be used to activate thecanister 12 and/or direct/observe diagnostic or operational tests. Afterimplantation, the programmer 22 may be used to non-invasively determinethe status and history of the implanted device. The programmer 22 incombination with the canister 12 may also allow annunciation ofstatistics, errors, history and potential problems to the user/medicalpractitioner, and may also allow for updating of programming in thecanister 12.

In some examples, the present invention may be implemented in a systemas shown in FIG. 2. In other examples, an implantable or wearablecardiac monitor may have multiple electrodes on a housing and/or lead todefine two or more sensing vectors. Leadless devices, such as leadlesscardiac pacemakers for implantation inside the heart, may have multiplesensing electrodes on or extending from a canister or housing to definemultiple sensing vectors. Wearable defibrillators or pacemakers may alsoprovide multiple cutaneous electrodes on the anterior and/or posteriorthorax of the patient, and may even include indifferent electrodeselsewhere such as on a limb. Transvenous and/or epicardial implantabledevices may have an active housing adapted for use in sensing along withplural electrodes for sensing on one or more leads, as is well known inthe art. For example, a transvenous device may have a right ventricularlead with atrial and ventricular sensing electrodes as well as anindifferent electrode on the canister. Alternative devices may also orinstead use a lead beneath the ribs and outside of the heart such as ina substernal location.

Specific to the device shown in FIG. 2, unlike prior art defibrillatorsand pacemakers that included electrodes in or on the heart, the deviceuses only far-field electrodes outside the ribcage and away from theheart for detecting cardiac activity. This can make counting cardiaccycles more difficult, as the source of the detected signal may beharder to distinguish. For example, while a ventricular depolarizationdetected with a transvenous, intracardiac electrode may be quite sharpand narrow in width, the same signal will be wider and less sharp whendetected in the far field. In some field products, T-wave overdetectionhas been observed in which individual cardiac cycles are counted twice,with a detection occurring on the R-wave and again on the T-wave. Whilesignificant effort is expended to avoid and/or identify and correct suchoverdetection, further improvements are desirable.

FIG. 3 provides a highly schematic depiction of an illustrative cardiacrhythm management device. The device 50 includes a plurality ofelectrodes 52, 54, 56, which may be provided on the housing of thedevice and/or in association with one or more leads. A multiplexor 60may be provided to couple selected subsets of the electrodes 52/54/56 tothe interior circuitry of the system. A set of DC blocking capacitorsmay be provided at 62 and the remaining signal passed onto an amplifieror plurality of amplifiers at 64. If desired elements 62 and 60 may beprovided in opposite arrangement, or multiple DC blocking subcircuits 62may be provided.

The amplifier stage 64 is associated with filter 66, which may be, forexample, a low pass filter designed to block out higher frequencysignals prior to reaching the analog-to-digital conversion (ADC) circuit68. Any suitable ADC circuit 68 may be used, including a wide array ofsuch devices known in the art including delta-sigma, successiveapproximation, Wilkinson, ramp-compare, delta encoded, pipeline,integrating, etc. The digital signal may then be notch filtered asindicated at 70 using, for example, a microprocessor or, in someembodiments, one or more digital signal processing chips.

At this point the signal can take two separate paths. In one path, thesignal from the notch filter 70 goes directly to a morphology block 74,and is also fed to a cardiac cycle detector 76. The morphology block 74is configured to store a set of data associated with a particularcardiac cycle and perform measurements and/or comparisons of the dataincluding, for example, measurement of signal width and/or amplitude,slew rate, or other measurable features, as well as comparison to one ormore static or dynamic templates using methods such as those in U.S.Pat. Nos. 7,477,935 and 7,376,458. The cardiac cycle detector 76 may bean R-wave detector or QRS complex detector using, for example, methodsshown in U.S. Pat. Nos. 8,565,878 and/or 5,709,215, the disclosures ofwhich are incorporated herein by reference. Though not shown, detectedcardiac cycles may be certified by removing noise and/or overdetectionusing methods such as shown in U.S. Pat. Nos. 7,248,921, 8,160,686,and/or 8,160,687.

In the other path, the signal from the notch filter goes through a highpass filter stage 72 before going, again, to morphology block 74 and thecardiac cycle detector 76. The two “paths” may operate in parallel, orthe device may be configured to engage the circuitry to use one path fora first period of time and the other path for a second period of time toallow later comparison.

The outputs of the cardiac cycle detector 76 and morphology block 74 areprovided to a rhythm analysis block 78. The rhythm analysis block 78 mayuse various known methods for analyzing a patient's cardiac rhythmusing, for example, a rate as calculated using the outputs of thecardiac cycle detector 76, as well as various shape features generatedusing the morphology block 74. Combinations of rate, width, amplitude,and matching to a template can be used to determine what is going on inthe patient's heart. There may additionally be feedback paths tomanipulate the operation of, for example, the multiplexor 60, notch 70,switch 82, and each of the morphology block 74 and cardiac cycledetector 76.

In some examples, as indicated, block 78 is performed by a controller 80which may wake up in response to the output of the cardiac cycledetector 76. The controller 80 may be a microcontroller ormicroprocessor, for example, with associated memory for storing in anon-transitory medium instruction sets for performing various analyses.In other examples, different architectures may be used, for example,block 68 may be an ADC that is part of the controller 80, with each ofblocks 70, 72, 74, 76 and 78 being performed by operable blocks of codestored in memory and accessed by the controller 80.

A switch is provided at 82 to allow selection between the signal comingout of the notch filter 70 or the signal from the additional highpassfilter stage 72 for use in each of the morphology block 74 and thecardiac cycle detector. In some examples, if the highpass filter block72 is not in use, it may also be powered down. In some examples, acombination of the notch 70 and highpass filter stage 72 operates as afirst filtering configuration, and the notch 70 without the highpassfilter stage 72 operates as a second filtering configuration, in whichthe first filtering configuration includes additional filtering relativeto the second filtering configuration.

FIG. 4 shows an illustrative method in block flow form. This example 100begins with gathering data in a cardiac rhythm management device inwhich at least one high pass (“HP”) filter is off, as indicated (inshort hand) at 102.

As used in one example, a standard or baseline filtering approach istaken with a pass band in the range of about 3 Hz to about 40 Hz, withadditional notch filtering for line signals at 50 or 60 Hz. In thisexample, the HP filter is a high pass filter with a corner frequency at9 Hz that is not on in the default approach, but which is available tobe turned on if desired in addition to the default filtering. With theadditional HP filter on, the passband would then be in the range ofabout 9 Hz to about 40 Hz, with additional filters again at the linefrequencies (50 or 60 Hz), and another filter at 3 Hz that sits outsideof the pass band.

These specific corner points for each filter may be varied in otherexamples. For example, a 4 Hz to 25 Hz passband may serve as default,with an extra 8 Hz filter applied optionally in one example. In anotherexample, a 2 Hz to 50 Hz passband may be used by default with anadditional high pass filter at about 7 Hz. These boundaries andpassbands are noted here for cardiac signal purposes in particular.Those skilled in the art will recognize that other passbands andadditional filter locations may be useful in other contexts, forexample, when monitoring muscular or neurological activity in differentparts of the body such as the diaphragm, digestive tract, spinal column,skeletal muscles, Vagus nerve, or brain.

A measure of amplitude of the gathered data is compared to a firstthreshold at 104. The measure of amplitude may take several forms. Insome examples, cardiac cycle detection is performed to identify maximumpeaks associated with cardiac cycles in the gathered data, and themaximum peaks are measured and/or averaged for comparison to the firstthreshold. In other examples, an average signal strength, such as aroot-mean-square (RMS) amplitude is determined for the gathered data.

In one example, the first threshold is equal to about six times thenoise floor of a given system. Other ratios may be used. In oneillustrative embodiment, the first threshold is set to about 500microvolts, for a system having an 80 microvolt noise floor. Thecomparison at 104 is intended ensure that the existing cardiac signalamplitude is well above the noise floor, since a high pass filter asenvisioned in this example may well attenuate the cardiac signal.Therefore, if the amplitude measure is not greater than the threshold at104, the high pass filter is left off, as indicated at 106.

If the test at 104 is passed, additional data is gathered, this timewith the HP filter on as indicated at 108. Another comparison of anamplitude measure to a threshold is performed, as indicated at block110. In one example, the amplitude measure at 110 is again a measure ofthe R-wave, while the threshold, TH2 is now a lower threshold, such asthree times the noise floor, rather than six times the noise floor aspreviously discussed. As noted, other ratios may be used instead. If thesecond test at 110 is passed, then the HP filter is enabled orturned/left on 112. Otherwise, the HP filter is turned off or disabled,at 106. Returning to the example where the first threshold was 500microvolts in a system having an 80 microvolt noise floor, in anexample, the comparison at 110 uses the second threshold set to 250microvolts, or about three times the noise floor. Other boundaries maybe used.

FIG. 5 shows an illustrative method in block blow form. The method 150begins with the HP filter off, as indicated at 152. In this example, atleast two sensing vectors are made available for use by the device;here, the next step is to perform vector selection, as indicated at 154.Vector selection may include operating a cardiac cycle detection methodto identify a plurality of cardiac cycles and generate measurements ofR-wave amplitude and/or signal to noise ratio, which may be assessedindependently or combined together using various scoring methods. Anysuitable vector selection method may be performed; some examples are inU.S. Pat. Nos. 7,392,085, 7,623,909, and 8,200,341, the disclosures ofwhich are incorporated herein by reference. Vector selection may bereassessed if sensing signal quality drops or if other conditions aremet, such as explained in U.S. Provisional Patent Application62/245,757, and multiple vectors may be combined as explained in U.S.Provisional Patent Applications 62/245,738, 62/245,762, and 62/245,729,the disclosures of which are incorporated herein by reference. Whichevervector(s) is (are) selected is stored as Result 1, at 156.

Next, the HP filter is turned on, at 160, and vector selection is againperformed as indicated at 162, this time using signals as filtered bythe HP filter. The outcome of the second vector selection 162 is storedas result 2, at 164. These results are then compared at 166. If there isa match, that is, if the same sensing vector is chosen by bothoperations, then the HP filter is enabled, as indicated at 170. IfResult 1 and Result 2 do not match, then the HP filter is disabled asindicated at 172.

In an example, the vector selection performed at block 154 may rely oneach of signal to noise ratio and the amplitude of cardiac signals(e.g., as shown in U.S. Pat. No. 7,623,909). However, in some examples,since the HP filter is added in before vector selection at 162, onlyamplitude needs to be assessed. In other examples, the vector selectionperformed in each of blocks 154 and 162 is the same. In another example,if the signal to noise ratio is calculated at 154 and a very high signalto noise ratio is found, the inclusion of an HP filter may beunnecessary and so blocks 160/162 could be bypassed in response.

There are several variants on the method of FIG. 5. In one variation, aparallel processing method is performed in which vectors are selectedwith the HP filter on and off, and sensing/detection of cardiac cyclesare performed on each of the two signals in parallel. The resultingcardiac signal detections are stored one-by-one, in temporally alignedfashion, at blocs 156 and 164. If the two sets of signal detectionsmatch—that is, if they are generally equal in number and occur atsimilar points in time, this indicates that the signal as detected withthe HP filter on is detected much the same as that with the HP filteroff, allowing for the HP filter to be enabled at 170. If there is amismatch, this may be construed, in one example, as indicating thathaving the HP filter on is creating difficulties and therefore the HPfilter is disabled at 172. In an alternative example, physicianassessment may be requested to determine which of the HP filtered andnot-filtered version of the signal is generated correct cardiac signaldetection if there is a mismatch.

In an example, with reference to FIG. 5, result 1 at 156 may be a ratioof the average R-wave amplitude to the RMS signal for the vector pickedat 154 while the HP filter is off. Continuing this example, result 2 at156 may be a ratio of the average R-wave amplitude to the RMS signal forthe vector picked at 162 while the HP filter is on. Whichever ratio islarger will determine whether the HP filter is enabled 170. For example,if the ratio is larger with the HP filter on, then the HP filter wouldbe enabled. When such a comparison is made, the boundary conditionsnoted with respect to FIG. 4 may be used as well, to ensure that theaverage R-wave amplitude with the HP filter on is well above the noisefloor.

FIG. 6 shows an illustrative method in block flow form. The method 200begins with the HP filter off, as indicated at 202. Data is gathered,for example by performing vector selection, or simply getting data onall vectors, and attributes of the signal as sensed with the HP filteroff are generated and stored, as indicated at 206. The HP filter is thenturned on at 208, and data is again gathered at 210 and attributes withthe HP filter on are generated, as indicated at 212. An assessment isthen made, at 220, as to how each of the sets of attributes suggest thesystem would perform with the HP filter off or on. The HP filter is theneither turned on, at 222, or turned off, at 224.

In one example, the assessment at 220 may be constructed to preferhaving the HP filter off. For example, the assessment at 220 may simplybe whether the signal attributes at 212 are suitable for use; if so,then HP on is set at 222. If not, the assessment at 220 may simply turnthe HP filter off, 224, or may also consider whether the attributes ofthe signal at 206 are adequate for use and, if not, an error flag orannunciator may be set to indicate that the system may not befunctional.

In another example, the assessment at 220 may compare a signal to noiseratio calculated at 206 with a signal to noise ratio calculated at 212.If the signal to noise ratio at 212 is better, and if the amplitude ofthe signal at 212 is adequate, then the HP filter is set to on, at 222.Otherwise, the HP filter is set to off at 224.

In another example, the data gathered at 204 and 210 may include datagenerated over time by analyzing, for example, in a parallel processingscheme, cardiac signals captured with and without the HP filter on for aperiod of time that includes a number of cardiac cycles. Theindividually detected cardiac cycles may be analyzed to determine whichof attributes 206 or attributes 212 suggests a likelihood of accuratedetection. Some indicators may be, for example:

-   -   Signal to noise ratio and/or amplitude may serve in several        examples, though more sophisticated approaches follow. To the        extent signal to noise ratio is a factor, it may be calculated        in any suitable manner such as, for example and without        limitation, by calculating a peak R-wave amplitude and an        average signal amplitude over a complete cardiac cycle and        comparing the two by division or subtraction; by calculated a        peak or average signal magnitude or amplitude for a QRS complex        and comparing to a peak or average signal amplitude or magnitude        for a period of time associated with a T-wave or the T-wave        itself    -   If a noise detection analysis is performed on detected cardiac        cycles, or on the signal generally, whichever of 206 or 212 has        fewer noise markers. For an example of noise analysis, see U.S.        Pat. No. 7,248,921, the disclosure of which is incorporated        herein by reference. In one example, a quantity of turning        points or inflection points in the sensed cardiac signal        associated with a cardiac cycle detection is compared to a        threshold and, if the threshold is exceeded, a noise detection        is declared.    -   If overdetection analysis is performed on detected cardiac        cycles, whichever of 206 or 212 has fewer overdetection markers.        For examples of overdetection analysis, see U.S. Pat. Nos.        8,160,686 and 8,160,687, the disclosures of which are        incorporated herein by reference. In one example, correlation        analysis is used and if a sequence of three correlations are        performed against a template with result of high correlation for        two detected cardiac cycles around low correlation for a third        cardiac cycle detection, the third cardiac cycle detection is        found to be overdetected. In another example, if the intervals        between detected cardiac cycle match a pattern for overdetection        of, for example, long-short-long (or more complex patterns may        be used), one or more detected cardiac cycles are declared to be        overdetected. In still another example, if two cardiac cycle        detections occur very close together in time with specific        morphology or polarity, double detection of a QRS complex may be        declared. In yet another example, a detected cardiac cycle is        compared to at least two preceding detected cardiac cycles and,        if the immediately preceding cycle detection does not match the        detected cardiac cycle, but the cycle detection two prior does        match the detected cardiac cycle, the immediately preceding        cardiac cycle detection is declared to be overdetected.    -   If R-wave and T-wave amplitudes can be estimated for cardiac        cycles, the ratio of R:T may be calculated, with a higher ratio        indicating likely better sensing. U.S. Pat. No. 7,623,909 shows        some examples of finding R:T ratios. For example, following a        cardiac cycle detection, a peak occurring during a first time        period (for example, the 200 to 300 milliseconds preceding and        following the cardiac cycle detection) may be presumed to be the        R-wave and a peak occurring during a second time period, such as        a time period starting 200 to 300 milliseconds after the cardiac        cycle detection and lasting about 300 milliseconds, may be        deemed to be the T-wave, assuming also that the actual cardiac        rate is less than 120 beats per minute or so.    -   If a morphology analysis block is available, signal attributes        may include calculation of the similarity of each detected        cardiac cycle to adjacent cycles and/or to a stored template. If        one or the other of blocks 206 and 212 shows a stronger        correlation over time, this may indicate which signal is better        functioning. U.S. Pat. Nos. 8,160,686 and 8,160,687 each discuss        different variants on comparison of detected cardiac cycles to        one or more static or dynamic template.    -   Again using a morphology analysis block, whether a high scoring        template comparison can be had using multiple cardiac cycle        signals may serve as another signal quality indicator using, for        example, the methods of U.S. Pat. Nos. 7,477,935 and 7,376,458,        the disclosures of which are incorporated herein by reference.        Other comparisons may be made as well at 220, and the invention        should not be understood as being limited to any of the above.

The above methods in FIGS. 4-6 may be performed while a patient isin-clinic or ambulatory. Because signal quality data is being gathered,it may be suitable to limit some methods to in-clinic use undersupervision of a physician, so that patient activity or external events(such as working next to high power equipment) does not create untowardoutcomes. In some examples, a patient activity monitor may be used, suchas an accelerometer, and the methods may be limited to performance whilethe patient is found to be at rest or sleeping.

FIG. 7 shows another illustrative method in block flow form. Thisexample is designed for operation while the patient is ambulatory, asindicated at 250, and operates with the HP filter on, as noted at 264.The activity here includes ordinary cardiac cycle detection at 260 andanalysis at 262, which may take any of numerous forms known in the artand implemented in various commercially available cardiac rhythmmanagement devices such as implantable cardioverter defibrillators, theS-ICD System, cardiac resynchronization devices, pacemakers, wearabledefibrillators, and other products.

The method diverges from these prior implementations by noting that theHP filter is on at 264 and performing analysis to ensure that thepatient's sensed signals are not becoming inadequate. A first tier checkis noted at 266, where a count of low amplitude signals is made. Thecount of low amplitude signals 266 may call for a set of consecutivedetected cardiac cycles to have low amplitude, or a set of sensed datato remain below a threshold, yielding consecutive data 270. Alternative,the count of low amplitude signals 266 may look at a ratio of lowamplitude events within a set of events or time; for example, if 10 of18, or some other ratio, of consecutive detected events have anamplitude below a threshold.

If low amplitude is found at 266, in one example, the HP filter issimply turned off, at 272, in the hopes that this will improveamplitudes and move away from the noise floor. In another example, atime-based, second check is also performed, as noted at 274. In thisexample, if block 266 is satisfied, then a long pause, or several longpauses, may be sought out, as indicated at 274. This additional step at274 may be provided to ensure that the low amplitude signal is actuallyaffecting sensing by causing what may appear to be undersensing. If thelong pause(s) requirement at 274 is met, then the HP filter is turnedoff at 272. If either of blocks 266 or 274 fail, the method returns tothe ordinary detection/analysis cycle 260/262.

In one example, block 266 calls for a consecutive set of 1 to 100 beatswith amplitude below a threshold in the range of three to six times thenoise floor of a system. In the embodiment tested, the noise floor wasat 80 microvolts and the low amplitude thresholds tested were 250 and500 microvolts, with sets of 1, 5 and 100 beats tested. Lower numbersand higher thresholds will turn the HP filter off more readily. In thisexample, block 274 was omitted/bypassed.

In another example, block 266 calls for an X out of Y approach, or ratio268. Tested quantities were 10/24 and 18/24, with the amplitudeboundaries again at three to six times the noise floor of the testedsystem. The lower quantity for X would again be more aggressive, howeverit would take a longer period of time to fill the buffer with such anumber of events than some of the shorter contiguous event tests (1 and5) noted just above. In this example, block 274 was omitted/bypassed.

In another example, a test called for five consecutive events having anamplitude below three times the noise floor (250 microvolts in a systemwith an 80 microvolt noise floor, in this example), for block 266, andalso called for at least two out of five previously detected cardiaccycles to be separated by intervals of more than 1200 milliseconds. Infurther testing, the interval was extended to 1400 milliseconds. In someembodiments, a timeout may take place without a detected cardiac event;in one example, a two-second timeout takes place if there is no detectedcardiac cycle, resetting a detection timer to zero. In this example, ifthe signals sensed during the two second period leading to the timeoutfail to exceed the amplitude threshold, the two second period may becounted as one of the contiguous low amplitude detected cardiac cycles.

Specific references to a particular implementation should be understoodas illustrative; it is sufficient that a process is disclosed in FIG. 7whereby low amplitude or low amplitude in combination with long pause(s)may be assessed to determine that the HP filter can be disabled at block272.

FIG. 8 provides another depiction of an illustrative cardiac rhythmmanagement with functional blocks and data flow connections shown. Theillustrative device 300 includes a plurality of electrodes 302 coupledto input/output (I/O) circuitry at 310, which may include switches or amultiplexor that facilitate vector selection 312 to choose a preferredsensing vector from among the available electrode pairs. From the I/Ocircuit 310, the signal proceeds to a filter block 320. Filtering mayinclude or exclude a high pass (HP) filter 322 in addition to standardfiltering 324. The filtered signal from block 320 goes to a detectionblock 330, where individual cardiac cycles are detected by, for example,comparing a sensed signal to a time-varying amplitude threshold.Intervals between the detected cardiac cycles are then analyzed forcertification at 332 by, for example, eliminating noise and/oroverdetection. The overall cardiac rhythm can then be analyzed at 334using the certified intervals from block 332.

Each of blocks 330, 332 and 334 may generate data for use in a feedbackloop at 340 that can operate a filter selector at 350 and/or a filterdisabling functional block at 352. For example, filter selection 350 mayoperate using the methods shown above in FIGS. 4-6. Filter disable 352may operate as shown in FIG. 7. The filter selection block 350 andfilter disable block 352 determine whether the filter 320 uses standardfiltering 324 alone or in conjunction with the addition a high passfilter 322. The output signal from the filter block 320 may also be usedby one or both of blocks 350/352 to analyze the signal as filtered.

The device may also include a number of other functional blocks, such asa power block 360, which may include a rechargeable or primary cellbattery, or a super capacitor, or a circuit for receiving power from aremote source such as a coil for receiving power via inductive linkage.A memory 362 is shown and may include suitable random access or readonly memory, and/or solid state or flash memory, or other memorycircuits and chips. A therapy circuit 364 may be provided and mayinclude, for example, an output capacitor and charger for deliveringhigh voltage output (defibrillation, for example), or lower powercircuitry for providing output pacing therapy, or a driver for anactuator to deliver a therapeutic substance, for example. The therapycircuitry 364 may be coupled to the I/O 310. Telemetry circuitry 366 maybe provided to, for example, facilitate wireless RF or inductivetelemetry, or conducted communication, with other devices. Cellular orother communication capabilities may be supported in block 366.

A centralized control module 370 may also be provided, for example, amicrocontroller or microprocessor may be included. Several of thefunctional blocks shown may be provided as dedicated circuits, whileothers may be performed in a microcontroller using stored instructionsets. The description of FIG. 3, above, provides one example for anarchitecture.

In an example, vector selection block 312 may represent a module withinthe controller 370 for providing outputs to configure the I/O circuitry310, which would be provided as a dedicated or separate circuitry. Thefilter block 320 may include analog and/or digital elements as dedicatedASIC and discrete components, and may integrate therein amplificationand analog-to-digital conversion, all of which may operate together andinteract in various ways. The filter selector and filter disable blocksat 350, 352 may again be modules within the control block 370 andoperate as modules of instruction sets for controlling the operation ofthe filter block 320.

The detection block 330 may be a dedicated ASIC or set of functionaldiscrete components or circuits within an ASIC, while certification mayinclude multiple elements that appear in discrete components andcircuits within an ASIC while also representing modules of implementableinstruction sets operated by the control circuit 370. Analysis of therhythm 334 likely occurs primarily within the control block 334, aswould the analysis in the feedback block 340. The instruction sets foroperation by the control circuit may be stored in memory in anon-transitory form, such as in a flash memory location or in othercontroller readable memory.

Some implementations include operational circuitry for receiving asignal from implantable electrodes, processing the signal and analyzingthe processed signal to make decisions such as whether to store data ordeliver therapy. Operational circuitry may be housed in a canister orcanisters. The operational circuitry may include a controller (such as amicrocontroller or microprocessor, or simply an application specificintegrated chip (ASIC) such as an analog, mixed signal, or digitalASIC). The operational circuitry may include suitable analog and/ordigital circuits needed for signal processing, memory storage andgeneration of high-power electrical, low-power electrical and/ornon-electrical outputs. The operational circuitry may include suitablebattery technology for an implantable device (rechargeable or primarycell), with any of numerous examples well known in the art, and may usevarious capacitor technologies to assist in the short term build-upand/or storage of energy for defibrillation or other output purposes.

Implantable or wearable components may be manufactured withbiocompatible materials suitable for implantation or tissue contact,such as those widely known, along with coatings for such materials,throughout the art. For example, implantable devices can be made usingtitanium, with a titanium nitride or iridium oxide (or other material)coating if desired, and implantable leads can be formed with abiocompatible material such as a polyether, polyester, polyamide,polyurethane, polycarbonate, silicon rubber and blends or copolymersthereof. Alternatively, other biocompatible materials such as silver,gold, titanium, or stainless steel such as MP35N stainless steel alloy,or other materials may be used.

In some examples, the system may include one or more sensors to detectsignals in addition to the cardiac electrical signal that can becaptured using selected combinations of implantable or wearableelectrodes. Such additional sensors may include, for example,temperature sensors, accelerometers, microphones, optical sensors andchemical sensors, among others. The programmer 22 and implantable device12 (FIG. 2) may communicate with one another using, for example andwithout limitation, inductive or RF telemetry, or any other suitablecommunication solution, including conducted communication. The presentinvention may be embodied in a system having any such characteristics.

In the following non-limiting examples, where a flow diagram isreferenced relative to a means term or device element, it may beunderstood that the means or device may be a circuit having logic,analog and or digital functional elements configured to perform anillustrative step or may comprise a stored instruction set for executionby a controller or processor of a given device.

A first non-limiting example takes the form of a cardiac rhythmmanagement device comprising plural sensing electrodes for capturing acardiac signal and operational circuitry coupled to the plural sensingelectrodes for analyzing the cardiac signal. FIG. 2 shows an example ofsuch a system having electrodes available for sensing at each of 12, 16,18 and 20, and operational circuitry contained in the canister 12 asdescribed above and also shown in FIG. 3 and FIG. 8. In the firstnon-limiting example, the operational circuitry comprises the following:filter means for filtering the captured cardiac signal according to afirst approach and a second approach, the second approach applying anadditional high pass filter relative to the first approach (see FIG. 3,with filtering at 66 and 72 where the switch 82 determines whether theadditional filter at 72 is included in the signal passed on formorphology and/or detection analysis; also FIG. 8 with filter 320 andselection block 350 controlling whether standard filtering 324 is usedalone or with high pass filter 322); selector means coupled to thefilter means for determining whether to select the first approach or thesecond approach for the filter means (switch 82, for example, as shownin FIG. 3, and/or selection block 350 in FIG. 8), wherein the selectormeans is configured to determine a first amplitude of the capturedcardiac signal, post filtering via the first approach, and compare thefirst amplitude to a first threshold (such configuration of the selectormeans is illustrated in the flow diagram of FIG. 4 and may beimplemented in hardware or as instructions for operation by a controlleror processor for example and or applied in FIG. 8 via controller 370 orfilter block 320 with filter selection block 350) and: if the firstamplitude exceeds the first threshold, enable the second approach foruse in cardiac signal analysis (In FIG. 4, Yes at block 104 passing toblock 108, implemented for example in the systems shown in FIG. 3 orFIG. 8); or if the first amplitude does not exceed the first threshold,disable the second approach for use in cardiac signal analysis (In FIG.4, No at block 104 leading to block 106 where the HP filter is turnedoff, implemented for example in the systems shown in FIG. 3 or FIG. 8);and cardiac cycle detector means for comparing a received cardiacsignal, as filtered by one of the first or second approaches, to adetection threshold and declaring a new cardiac cycle when the receivedcardiac signal exceeds the detection threshold (detection means areillustratively shown at FIG. 3, block 76 and again in FIG. 8, block330).

A second non-limiting example take the form of a cardiac rhythmmanagement device as in the first non-limiting example wherein theselector means is further configured, subsequent to enabling the secondapproach for use in cardiac signal analysis, to determine a secondamplitude of the captured cardiac signal after filtering via the secondapproach, and compare the second amplitude to a second threshold, thesecond threshold being lower than the first threshold, and, if thesecond amplitude does not exceed the second threshold, to disable thesecond approach for use in cardiac signal analysis. Such means areshown, for example, in FIG. 4, block 110 and 112 or 106, implemented forexample in the systems shown in FIG. 3 or FIG. 8 such as by using thefeedback block 340 as a separate circuit block or ASIC and/or viainstructions operated by the controller or processor 370.

A third non-limiting example takes the form of a cardiac rhythmmanagement device as in the second non-limiting example, furthercomprising disabling means for disabling the second approach, after ithas been selected by the selector means, wherein the disabling means isconfigured to determine a third amplitude of the captured cardiacsignal, as filtered via the second approach, and compare the thirdamplitude to a third threshold, and, if the third amplitude does notexceed the third threshold, disable the second approach. Disabling meansare highlighted at 352 in FIG. 8 taking information from the feedback at340 which can implement the methods of FIG. 7 where the low amplitudeblock 266 facilitates a decision to turn off the HP filter at 272.

A fourth non-limiting example takes the form of a cardiac rhythmmanagement device as in the second non-limiting example furthercomprising disabling means for disabling the second approach, thedisabling means comprising: interval means to analyze intervals betweencardiac cycles detected by the detection means and determining whetherplural such intervals exceed one or more predefined thresholds and, ifso, to declare long pauses have occurred; amplitude means for observingwhether one or more amplitudes associated with one or more cardiaccycles detected by the detection means fail to meet one or more minimumamplitude thresholds and, if so, to declare low amplitude; and thedisabling means is configured to disable the second approach if bothlong pauses and low amplitude have been declared at the same time.Example amplitude and interval means are illustrated in FIG. 7 at blocks266 and/or 274, and disabling means at block 272, with the amplitude andinterval assessments forming operational parts of the feedback 340 inFIG. 8 and disabling block at 352 of FIG. 8.

A fifth non-limiting example takes the form of a cardiac rhythmmanagement device as in the second non-limiting example, furthercomprising disabling means for disabling the second approach, thedisabling means comprising interval means to analyze intervals betweencardiac cycles detected by the detection means and determining whetherplural such intervals exceed one or more predefined thresholds and, ifso, to declare long pauses have occurred; and the disabling means isconfigured to disable the second approach long pauses have beendeclared. Interval analysis is shown in FIG. 7 at 274 in relation toidentifying a long pause (or long pauses), triggering disabling at 272;such may be operational parts of the feedback 340 in FIG. 8 anddisabling block at 352 of FIG. 8.

A sixth non-limiting example takes the form of a cardiac rhythmmanagement device as in the second non-limiting example, furthercomprising disabling means for disabling the second approach, thedisabling means comprising amplitude means for observing whether one ormore amplitudes associated with one or more cardiac cycles detected bythe detection means fail to meet one or more minimum amplitudethresholds and, if so, to declare low amplitude; and wherein thedisabling means is configured to disable the second approach if lowamplitude has been declared. Amplitude is assessed at 266 in FIG. 7 andlinked to disabling at 272; such may be operational parts of thefeedback 340 in FIG. 8 and disabling block at 352 of FIG. 8.

A seventh non-limiting example takes the form of a cardiac rhythmmanagement device comprising plural sensing electrodes for capturing acardiac signal (for example as shown in FIG. 2) and operationalcircuitry coupled to the plural sensing electrodes for analyzing thecardiac signal (for example as shown in FIGS. 3 and/or 8), theoperational circuitry comprising the following: filter means forfiltering the captured cardiac signal according to a first approach anda second approach, the second approach applying an additional high passfilter relative to the first approach (for example, FIG. 3 with filtersat 66 and the additional highpass at 72; also FIG. 8 at 320 with filteroptions at 322 and 324); and selector means coupled to the filter meansfor determining whether to select the first approach or the secondapproach for the filter means (selections illustrated using a switch at82 in FIG. 3, or the selection and disable blocks at 350, 352 in FIG.8), wherein the selector means is configured to operate the device tocapture data using each of the first approach and the second approach,to analyze the data captured with each of the first and secondapproaches, and to determine which of the first approach or secondapproach yields more suitable sensing data (for example, in FIG. 5,vector selection may be performed to yield results at 156, 164 with thedifferent filters chosen and then compared together at 166; in addition,in FIG. 6, attributes are measured at 206, 212 in and assessed at 220).

An eighth non-limiting example takes the form of a cardiac rhythmmanagement device as in the seventh non-limiting example, furthercomprising vector selection means for performing a vector selectionsequence using signals from at least first and second sensing vectorsdefined by the plurality of electrodes, wherein the selector means isconfigured to activate the vector selection means with the firstapproach enabled to yield a first selected vector, and again with thesecond approach enabled to yield a second selected vector, and theselector means is configured to determine which of the first approach orsecond approach yields more suitable sensing data by assessing: a)whether the first selected vector and the second selected vector are thesame sensing vector; and b) whether an amplitude measure for the secondselected vector exceeds an amplitude threshold; such that, if both a)and b) are true, the selector means is configured to select the secondapproach, and otherwise the selector means is configured to select thefirst approach. For example, FIG. 5 shows that vector selectioncapability is called upon at blocks 154 and 162 to provide outputs orresults at 156, 164, respectively for comparison at block 166 and use inenabling or disabling the filtering approach including an extra highpass filter at 170, 172; FIG. 8 illustrates the inclusion of vectorselection block 312 used to control the input/output subcircuit 310which can then drive the feedback loop at 340 in an example, as managedby the controller/processor 370).

A ninth non-limiting example takes the form of a cardiac rhythmmanagement device as in the seventh non-limiting example furthercomprising cardiac cycle detector means for comparing a received cardiacsignal, as filtered by one of the first or second approaches, to adetection threshold and declaring a new cardiac cycle when the receivedcardiac signal exceeds the detection threshold; wherein the selectormeans is configured to operate the cardiac cycle detector as follows: ina first data stream, on data filtered using the first approach; and in asecond data stream, on data filtered using the second approach; to yieldtwo sets of detected cardiac cycle data, wherein the selector means isconfigured to align the two sets of data and determine which of thefirst approach and second approach is providing more accurate cardiaccycle detection. For example, FIG. 6 shows data analysis that mayperform the gathering and attribute calculations for a first data streamvia the combination of blocks 204, 206, and a second data stream at 210,212 with the HP filter on, for provision to an assessment block at 220then driving the determination of which filter approach to select asbetween blocks 222 and 224; such may be used in FIG. 3 with dataprovided to the detector block 76 to generate cardiac cycle data, andalso in FIG. 8 with the feedback at 340 observing attributes from thedetection block 330 which may operate on multiple data streams at oncein a parallel processing approach or may alternatively operate insequential fashion on different sets of data.

A tenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the ninth non-limiting example, furthercomprising a noise identifier for determining whether one or moredetected cardiac cycles are noisy; wherein the selector means isconfigured to use the noise identifier to select whichever of the firstand second approaches yields fewer noisy detected cardiac cycles. Suchis illustrated in FIG. 8 where the certification of intervals at 332 canparallel process, or sequentially process, detected cardiac cycles fromblock 330 using noise analysis, as described above in several examples.

An eleventh non-limiting example takes the form of a cardiac rhythmmanagement device as in the ninth non-limiting example, furthercomprising an overdetection identifier for determining whether one ormore detected cardiac cycles are overdetected; wherein the selectormeans is configured to use the overdetection identifier to selectwhichever of the first and second approaches yields fewer overdetectedcardiac cycles. Such is illustrated in FIG. 8 where the certification ofintervals at 332 can parallel process, or sequentially process, detectedcardiac cycles from block 330 using overdetection analysis, as describedabove in several examples.

A twelfth non-limiting example takes the form of a cardiac rhythmmanagement device as in the ninth non-limiting example, furthercomprising wave identifier means for identifying R-waves and T-wavesassociated with individual detected cardiac cycles and calculating anR:T ratio for each of the first and second approaches; wherein theselector means is configured to use the wave identifier to selectwhichever of the first and second approaches yields a larger R:T ratio.For example, a wave identifier may form part of the detection block 330and/or certification block 332 shown in FIG. 8 by, for example,differentiating R and T waves from one another using amplitude and/ortiming thresholds or by reference to secondary signals which can alignthe R-wave to cardiac contraction using heart sounds or blood pressuremetrics, or pulse oximetry to identify blood flow, from which T-waverepolarization would be separated in time; such can be implemented inthe Feedback loop 340 to control filter selection and/or disablingblocks 350, 352.

A thirteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the seventh non-limiting example, wherein theselector means is configured to determine whether an amplitude measureof the signal as sensed using the first approach exceeds a firstthreshold and, if not, identify the first approach as yielding moresuitable sensing data. For example, an amplitude measure may be one ofthe attributes generated at blocks 204 and 210 in FIG. 6 and providedvia blocks 206, 212 to the assessment block at 220, using for example amethod as illustrated in FIG. 4 at blocks 102/104, performed by thefeedback loop, for example, at 340 in FIG. 8 to then control the filterselection and disabling blocks 350, 352.

A fourteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the thirteenth non-limiting example wherein theselector means is configured such that, if the amplitude measure of thesignal as sensed using the first approach does exceed the firstthreshold, the selector means is further configured to determine whetheran amplitude measure of the signal as sensed using the second approachexceeds a second threshold and: if the signal as sensed using the secondapproach exceeds the second threshold, to identify the second approachas yielding more suitable sensing data; and otherwise to identify thefirst approach as yielding more suitable sensing data. For example, anamplitude measure may be one of the attributes generated at blocks 204and 210 in FIG. 6 and provided via blocks 206, 212 to the assessmentblock at 220, using for example a method as illustrated in FIG. 4 atblocks 108/110, performed by the feedback loop, for example, at 340 inFIG. 8 to then control the filter selection and disabling blocks 350,352.

A fifteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the eighth to fourteenth non-limitingexamples further comprising disabling means for controlling thefiltering means and disabling the second approach if a combination ofsensed amplitudes with the second sensing approach and intervals betweencardiac event detections detected on a signal filtered using the secondapproach suggest possible undersensing. For example, FIG. 7 shows such amethod and may be implemented by the feedback loop for example at 340 inFIG. 8.

A sixteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the first fifteen examples, in which thefirst approach uses a bandpass filtering in the range of 3 to 40 hertz,and the second approach uses the same bandpass as the first approachwith an additional highpass filter at about 9 hertz. For example, FIGS.3 and 8 show systems having an additional highpass filter for swappinginto or out of the sensing process for cardiac signals.

A seventeenth non-limiting example takes the form of a cardiac rhythmmanagement device as in any of the first sixteen examples, furthercomprising therapy circuitry for providing a defibrillation stimuluswherein the device is a subcutaneous-only implantable defibrillator.Therapy circuitry is shown in FIG. 8 at 364, and a subcutaneous-onlyimplantable defibrillator is illustrated in FIG. 2.

An eighteenth non-limiting example takes the form of a cardiac rhythmmanagement device comprising plural sensing electrodes for capturing acardiac signal and operational circuitry coupled to the plural sensingelectrodes for analyzing the cardiac signal, the operational circuitryconfigured with a selectable filtering mode allowing filtering thecaptured cardiac signal according to a first approach and a secondapproach, the second approach applying an additional high pass filterrelative to the first approach, wherein the operational circuitry isconfigured to operate using the selectable filtering mode as follows:determining whether to select the first approach or the second approachby measuring a first amplitude of the captured cardiac signal, postfiltering via the first approach, and comparing the first amplitude to afirst threshold and: if the first amplitude exceeds the first threshold,enabling the second approach for use in cardiac signal analysis; or ifthe first amplitude does not exceed the first threshold, disabling thesecond approach for use in cardiac signal analysis; and detectingcardiac cycles by comparing a received cardiac signal, as filtered byone of the first or second approaches, to a detection threshold anddeclaring a new cardiac cycle when the received cardiac signal exceedsthe detection threshold.

A nineteenth non-limiting example takes the form of a cardiac rhythmmanagement device as in the eighteenth non-limiting example, wherein theoperational circuitry is further configured, subsequent to enabling thesecond approach for use in cardiac signal analysis, to: determine asecond amplitude of the captured cardiac signal after filtering via thesecond approach; compare the second amplitude to a second threshold, thesecond threshold being lower than the first threshold; and, if thesecond amplitude does not exceed the second threshold, disable thesecond approach for use in cardiac signal analysis. A twentiethnon-limiting example takes the form of cardiac rhythm management deviceas in the nineteenth non-limiting example, wherein the operationalcircuitry is further configured to disable the second approach, after ithas been selected for use, in response to determining that a thirdamplitude of the captured cardiac signal, as filtered via the secondapproach, fails to exceed a third threshold.

A twenty-first non-limiting example takes the form of a cardiac rhythmmanagement device as in the nineteenth non-limiting example, wherein theoperational circuitry is configured to disable the second approach byperforming the following: analyzing intervals between detected cardiaccycles and determining whether plural such intervals exceed one or morepredefined thresholds and, if so, to declare long pauses have occurred;observing whether one or more amplitudes associated with one or moredetected cardiac cycles fail to meet a minimum amplitude threshold and,if so, to declare low amplitude; and the operational circuitry isconfigured to disable the second approach if both long pauses and lowamplitude have been declared at the same time.

A twenty-second non-limiting example takes the form of a cardiac rhythmmanagement device as in the nineteenth non-limiting example, wherein theoperational circuitry is configured to disable the second approach byanalyzing intervals between detected cardiac cycles and determiningwhether plural such intervals exceed one or more predefined thresholdsand, if so, to declare long pauses have occurred and disable the secondapproach.

A twenty-third non-limiting example takes the form of a cardiac rhythmmanagement device as in the nineteenth non-limiting example, wherein theoperational circuitry is configured to disable the second approach byobserving whether one or more amplitudes associated with one or moredetected cardiac cycles fail to meet a minimum amplitude threshold and,if so, to declare low amplitude and disable the second approach. Atwenty-fourth non-limiting example takes the form of a cardiac rhythmmanagement device as any of the nineteenth to twenty-third non-limitingexamples, in which the first approach uses a bandpass filtering in therange of 3 to 40 hertz, and the second approach uses the same bandpassas the first approach with an additional highpass filter at about 9hertz.

A twenty-fifth non-limiting example takes the form of a cardiac rhythmmanagement device comprising plural sensing electrodes for capturing acardiac signal and operational circuitry coupled to the plural sensingelectrodes for analyzing the cardiac signal, the operational circuitryconfigured with a first filtering mode and a second filtering mode, thesecond filtering mode applying an additional high pass filter relativeto the first filtering mode, wherein the operational circuitry isconfigured to select between the first and second filtering modes by:capturing data using each of the first filtering mode and the secondfiltering mode; analyzing the data captured with each of the first andsecond filtering modes; and determining which of the first filteringmode or second filtering mode yields more suitable sensing data.

A twenty-sixth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-fifth non-limiting example, whereinthe operational circuitry is configured to: perform a vector selectionsequence using signals from at least first and second sensing vectorsdefined by the plurality of electrodes in a first iteration with thefirst filtering mode applied to yield a first selected vector, and in asecond iteration with the second filtering mode applied to yield asecond selected vector; determining which of the first filtering mode orsecond filtering mode yields more suitable sensing data by assessing: a)whether the first selected vector and the second selected vector are thesame sensing vector; and b) whether an amplitude measure for the secondselected vector exceeds an amplitude threshold; such that, if both a)and b) are true, the operational circuitry is configured to select anduse the second filtering mode for sensing cardiac signals, and otherwisethe operational circuitry is configured to select and use the firstfiltering mode for sensing cardiac signals.

A twenty-sixth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-fourth non-limiting example, whereinthe operational circuitry is configured to determine which of the firstand second filtering modes yields more suitable sensing data by:detecting cardiac cycles by comparing a received cardiac signal to adetection threshold and declaring a new cardiac cycle when the receivedcardiac signal exceeds the detection threshold in each of: a first datastream, on data filtered using the first filtering mode; and in a seconddata stream, on data filtered using the second filtering mode; andthereby yielding two sets of detected cardiac cycle data; aligning thetwo sets of detected cardiac cycle data; and determining which of thefirst filtering mode and second filtering mode is providing moreaccurate cardiac cycle detection.

A twenty-seventh non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-sixth non-limiting example, whereinthe operational circuitry is configured to determine whether one or moredetected cardiac cycles are noisy; and wherein the operational circuitryis configured to find that whichever of the first and second filteringmode has fewer noisy detected cardiac cycles yields more suitablesensing data. A twenty-eighth non-limiting example takes the form of acardiac rhythm management device as in the twenty-sixth non-limitingexample, wherein the operational circuitry is configured to determinewhether one or more detected cardiac cycles are overdetected; andwherein the operational circuitry is configured to find that whicheverof the first and second filtering modes has fewer overdetected cardiaccycles yields more suitable sensing data.

A twenty-ninth non-limiting example takes the form of a cardiac rhythmmanagement device as in the twenty-sixth non-limiting example, whereinthe operational circuitry is configured for: identifying R-waves andT-waves associated with individual detected cardiac cycles; calculatingan R:T ratio for each of the first and second filtering modes; andfinding that whichever of the first and second filtering modes yields alarger R:T ratio. A thirtieth non-limiting example takes the form of acardiac rhythm management device as in the twenty-fourth non-limitingexample, wherein operational circuitry is configured to determinewhether an amplitude measure of the signal as sensed using the firstfiltering mode exceeds a first threshold and, if not, identify the firstfiltering mode as yielding more suitable sensing data.

A thirty-first non-limiting example takes the form of a cardiac rhythmmanagement device as in the thirtieth non-limiting example wherein theoperational circuitry is further configured such that, if the amplitudemeasure of the signal as sensed using the first filtering mode doesexceed the first threshold, the operational circuitry is configured to:determine whether an amplitude measure of the signal as sensed using thesecond filtering mode exceeds a second threshold and: if the signal assensed using the second filtering mode exceeds the second threshold, toidentify the second filtering mode as yielding more suitable sensingdata; and otherwise to identify the first filtering mode as yieldingmore suitable sensing data. A thirty-second non-limiting example takesthe form of a cardiac rhythm management device as in the twenty-fourthnon-limiting example wherein the operational circuitry is configured todetermine whether possible undersensing is occurring and, if so, todisable the second filtering mode and activate the first filtering mode.

A thirty-third non-limiting example takes the form of a method ofoperation in a cardiac rhythm management device comprising pluralsensing electrodes for capturing a cardiac signal and operationalcircuitry coupled to the plural sensing electrodes for analyzing thecardiac signal, the operational circuitry configured with a selectablefiltering mode allowing filtering the captured cardiac signal accordingto a first approach and a second approach, the second approach applyingan additional high pass filter relative to the first approach, themethod comprising: determining whether to select the first approach orthe second approach by measuring a first amplitude of the capturedcardiac signal, post filtering via the first approach, and comparing thefirst amplitude to a first threshold and: if the first amplitude exceedsthe first threshold, enabling the second approach for use in cardiacsignal analysis; or if the first amplitude does not exceed the firstthreshold, disabling the second approach for use in cardiac signalanalysis; and detecting one or more cardiac cycles by comparing areceived cardiac signal, as filtered by one of the first or secondapproaches, to a detection threshold and declaring a new cardiac cyclewhen the received cardiac signal exceeds the detection threshold.

A thirty-fourth non-limiting example takes the form of a method as inthe thirty-third non-limiting example, further comprising, subsequent toenabling the second approach for use in cardiac signal analysis anddetecting one or more cardiac cycles therewith: determining a secondamplitude of the captured cardiac signal after filtering via the secondapproach; comparing the second amplitude to a second threshold, thesecond threshold being lower than the first threshold; and, if thesecond amplitude does not exceed the second threshold, disabling thesecond approach for use in cardiac signal analysis. A thirty-fifthnon-limiting example takes the form of a method as in the thirty-fourthnon-limiting example further comprising disabling the second approach,after it has been selected for use, in response to determining that athird amplitude of the captured cardiac signal, as filtered via thesecond approach, fails to exceed a third threshold.

A thirty-sixth non-limiting example takes the form of a method as in thethirty-third non-limiting example, further comprising, subsequent toenabling the second approach for use in cardiac signal analysis anddetecting two or more cardiac cycles having intervals therebetween:analyzing intervals between detected cardiac cycles and determiningwhether plural such intervals exceed one or more predefined thresholds;observing whether one or more amplitudes associated with one or moredetected cardiac cycles fail to meet a minimum amplitude threshold; andif plural intervals exceed the one or more predefined thresholds, andone or more detected cardiac cycles fail to meet the minimum amplitudethreshold while using the second approach, disabling the secondapproach. A thirty-seventh non-limiting example takes the form of amethod as in the thirty-third non-limiting example, further comprising,subsequent to enabling the second approach for use in cardiac signalanalysis and detecting two or more cardiac cycles having intervalstherebetween: analyzing intervals between detected cardiac cycles; anddetermining whether plural such intervals exceed one or more predefinedthresholds and, if so, disabling the second approach. A thirty-eighthnon-limiting example takes the form of a method as in the thirty-thirdnon-limiting example, further comprising, subsequent to enabling thesecond approach for use in cardiac signal analysis and detecting two ormore cardiac cycles having intervals therebetween, observing whether oneor more amplitudes associated with one or more detected cardiac cyclesfail to meet a minimum amplitude threshold and, if so, disabling thesecond approach. A thirty-ninth non-limiting example takes the form of amethod as in any of the thirty-third to thirty-eighth non-limitingexamples, wherein: the first approach uses a bandpass filtering in therange of 3 to 40 hertz; and the second approach uses a bandpassfiltering in the range of about 9 to 40 hertz.

A fortieth non-limiting example takes the form of a method of operationin a cardiac rhythm management device comprising plural sensingelectrodes for capturing a cardiac signal and operational circuitrycoupled to the plural sensing electrodes for analyzing the cardiacsignal, the operational circuitry configured with a selectable filteringmode allowing filtering the captured cardiac signal according to a firstapproach and a second approach, the second approach applying anadditional high pass filter relative to the first approach, the methodcomprising: filtering cardiac signals with the second approach andanalyzing the cardiac signals that have been filtered with the secondapproach to detect cardiac cycles; determining that conditions indicatea termination of the second approach is appropriate; and switching touse of the first approach for filtering the cardiac signals. Aforty-first non-limiting example takes the form of a method as in thefortieth non-limiting example, wherein the step of determining thatconditions indicate a termination of the second approach is appropriatecomprises: analyzing intervals between detected cardiac cycles anddetermining whether plural such intervals exceed one or more predefinedthresholds; observing whether one or more amplitudes associated with oneor more detected cardiac cycles fail to meet a minimum amplitudethreshold; and if plural intervals exceed the one or more predefinedthresholds, and one or more detected cardiac cycles fail to meet theminimum amplitude threshold while using the second approach, determiningthat conditions indicate a termination of the second approach isappropriate. A forty-second non-limiting example takes the form of amethod as in the fortieth non-limiting example, wherein the step ofdetermining that conditions indicate a termination of the secondapproach is appropriate comprises: analyzing intervals between detectedcardiac cycles; and determining whether plural such intervals exceed oneor more predefined thresholds and, if so, determining that conditionsindicate a termination of the second approach is appropriate. Aforty-third non-limiting example takes the form of a method as in thefortieth non-limiting example, wherein the step of determining thatconditions indicate a termination of the second approach is appropriatecomprises observing whether one or more amplitudes associated with oneor more detected cardiac cycles fail to meet a minimum amplitudethreshold.

Each of these non-limiting examples can stand on its own, or can becombined in various permutations or combinations with one or more of theother examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols. In this document, the terms “a” or “an” are used, as is commonin patent documents, to include one or more than one, independent of anyother instances or usages of “at least one” or “one or more.” Moreover,in the following claims, the terms “first,” “second,” and “third,” etc.are used merely as labels, and are not intended to impose numericalrequirements on their objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic or optical disks,magnetic cassettes, memory cards or sticks, random access memories(RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description.

The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow thereader to quickly ascertain the nature of the technical disclosure. Itis submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims.

Also, in the above Detailed Description, various features may be groupedtogether to streamline the disclosure. This should not be interpreted asintending that an unclaimed disclosed feature is essential to any claim.Rather, inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description as examples or embodiments,with each claim standing on its own as a separate embodiment, and it iscontemplated that such embodiments can be combined with each other invarious combinations or permutations. The scope of the invention shouldbe determined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

The claimed invention is:
 1. A cardiac rhythm management devicecomprising plural sensing electrodes for capturing a cardiac signal andoperational circuitry coupled to the plural sensing electrodes foranalyzing the cardiac signal, the operational circuitry configured witha selectable filtering mode allowing filtering the captured cardiacsignal according to a first approach and a second approach, the secondapproach applying an additional high pass filter relative to the firstapproach, wherein the operational circuitry is configured to operateusing the selectable filtering mode as follows: determining whether toselect the first approach or the second approach by measuring a firstamplitude of the captured cardiac signal, post filtering via the firstapproach, and comparing the first amplitude to a first threshold and: ifthe first amplitude exceeds the first threshold, enabling the secondapproach for use in cardiac signal analysis; or if the first amplitudedoes not exceed the first threshold, disabling the second approach foruse in cardiac signal analysis; and detecting cardiac cycles bycomparing a received cardiac signal, as filtered by one of the first orsecond approaches, to a detection threshold and declaring a new cardiaccycle when the received cardiac signal exceeds the detection threshold.2. A cardiac rhythm management device as in claim 1 wherein theoperational circuitry is further configured, subsequent to enabling thesecond approach for use in cardiac signal analysis, to: determine asecond amplitude of the captured cardiac signal after filtering via thesecond approach; compare the second amplitude to a second threshold, thesecond threshold being lower than the first threshold; and, if thesecond amplitude does not exceed the second threshold, disable thesecond approach for use in cardiac signal analysis.
 3. A cardiac rhythmmanagement device as in claim 1, wherein the operational circuitry isconfigured to disable the second approach by performing the following:analyzing intervals between detected cardiac cycles and determiningwhether plural such intervals exceed one or more predefined thresholdsand, if so, to declare long pauses have occurred; observing whether oneor more amplitudes associated with one or more detected cardiac cyclesfail to meet a minimum amplitude threshold and, if so, to declare lowamplitude; and the operational circuitry is configured to disable thesecond approach if both long pauses and low amplitude have been declaredat the same time.
 4. A cardiac rhythm management device as in claim 1,wherein the operational circuitry is configured to disable the secondapproach by analyzing intervals between detected cardiac cycles anddetermining whether plural such intervals exceed one or more predefinedthresholds and, if so, to declare long pauses have occurred and disablethe second approach.
 5. A cardiac rhythm management device as in claim1, wherein the operational circuitry is configured to disable the secondapproach by observing whether one or more amplitudes associated with oneor more detected cardiac cycles fail to meet a minimum amplitudethreshold and, if so, to declare low amplitude and disable the secondapproach.
 6. A cardiac rhythm management device as in claim 1 in whichthe first approach uses a bandpass filtering in the range of 3 to 40hertz, and the second approach uses the same bandpass as the firstapproach with an additional highpass filter at about 9 hertz.
 7. Acardiac rhythm management device comprising plural sensing electrodesfor capturing a cardiac signal and operational circuitry coupled to theplural sensing electrodes for analyzing the cardiac signal, theoperational circuitry configured with a first filtering mode and asecond filtering mode, the second filtering mode applying an additionalhigh pass filter relative to the first filtering mode, wherein theoperational circuitry is configured to select between the first andsecond filtering modes by: capturing data using each of the firstfiltering mode and the second filtering mode; analyzing the datacaptured with each of the first and second filtering modes; anddetermining which of the first filtering mode or second filtering modeyields more suitable sensing data.
 8. The cardiac rhythm managementdevice of claim 7 wherein the operational circuitry is configured to:perform a vector selection sequence using signals from at least firstand second sensing vectors defined by the plurality of electrodes in afirst iteration with the first filtering mode applied to yield a firstselected vector, and in a second iteration with the second filteringmode applied to yield a second selected vector; determining which of thefirst filtering mode or second filtering mode yields more suitablesensing data by assessing: a) whether the first selected vector and thesecond selected vector are the same sensing vector; and b) whether anamplitude measure for the second selected vector exceeds an amplitudethreshold; such that, if both a) and b) are true, the operationalcircuitry is configured to select and use the second filtering mode forsensing cardiac signals, and otherwise the operational circuitry isconfigured to select and use the first filtering mode for sensingcardiac signals.
 9. The cardiac rhythm management device of claim 7wherein the operational circuitry is configured to determine which ofthe first and second filtering modes yields more suitable sensing databy: detecting cardiac cycles by comparing a received cardiac signal to adetection threshold and declaring a new cardiac cycle when the receivedcardiac signal exceeds the detection threshold in each of: a first datastream, on data filtered using the first filtering mode; and in a seconddata stream, on data filtered using the second filtering mode; andthereby yielding two sets of detected cardiac cycle data; aligning thetwo sets of detected cardiac cycle data; and determining which of thefirst filtering mode and second filtering mode is providing moreaccurate cardiac cycle detection.
 10. The cardiac rhythm managementdevice of claim 9 wherein the operational circuitry is configured todetermine whether one or more detected cardiac cycles are noisy; andwherein the operational circuitry is configured to find that whicheverof the first and second filtering mode has fewer noisy detected cardiaccycles yields more suitable sensing data.
 11. The cardiac rhythmmanagement device of claim 9 wherein the operational circuitry isconfigured to determine whether one or more detected cardiac cycles areoverdetected; and wherein the operational circuitry is configured tofind that whichever of the first and second filtering modes has feweroverdetected cardiac cycles yields more suitable sensing data.
 12. Thecardiac rhythm management device of claim 9 wherein the operationalcircuitry is configured for: identifying R-waves and T-waves associatedwith individual detected cardiac cycles; calculating an R:T ratio foreach of the first and second filtering modes; and finding that whicheverof the first and second filtering modes yields a larger R:T ratio. 13.The cardiac rhythm management device of claim 7 wherein operationalcircuitry is configured to determine whether an amplitude measure of thesignal as sensed using the first filtering mode exceeds a firstthreshold and, if not, identify the first filtering mode as yieldingmore suitable sensing data.
 14. The cardiac rhythm management device ofclaim 13 wherein the operational circuitry is further configured suchthat, if the amplitude measure of the signal as sensed using the firstfiltering mode does exceed the first threshold, the operationalcircuitry is configured to: determine whether an amplitude measure ofthe signal as sensed using the second filtering mode exceeds a secondthreshold and: if the signal as sensed using the second filtering modeexceeds the second threshold, to identify the second filtering mode asyielding more suitable sensing data; and otherwise to identify the firstfiltering mode as yielding more suitable sensing data.
 15. The cardiacrhythm management device of claim 7 wherein the operational circuitry isconfigured to determine whether possible undersensing is occurring and,if so, to disable the second filtering mode and activate the firstfiltering mode.
 16. A method of operation in a cardiac rhythm managementdevice comprising plural sensing electrodes for capturing a cardiacsignal and operational circuitry coupled to the plural sensingelectrodes for analyzing the cardiac signal, the operational circuitryconfigured with a selectable filtering mode allowing filtering of thecaptured cardiac signal according to a first approach and a secondapproach, the second approach applying an additional high pass filterrelative to the first approach, the method comprising: determiningwhether to select the first approach or the second approach by measuringa first amplitude of the captured cardiac signal, as filtered using thefirst approach, and comparing the first amplitude to a first thresholdand: if the first amplitude exceeds the first threshold, enabling thesecond approach for use in cardiac signal analysis; or if the firstamplitude does not exceed the first threshold, disabling the secondapproach for use in cardiac signal analysis; and detecting one or morecardiac cycles by comparing a received cardiac signal, as filtered byone of the first or second approaches, to a detection threshold anddeclaring a new cardiac cycle when the received cardiac signal exceedsthe detection threshold.
 17. A method as in claim 16 further comprising,subsequent to enabling the second approach for use in cardiac signalanalysis and detecting one or more cardiac cycles therewith: determininga second amplitude of the captured cardiac signal after filtering viathe second approach; comparing the second amplitude to a secondthreshold, the second threshold being lower than the first threshold;and, if the second amplitude does not exceed the second threshold,disabling the second approach for use in cardiac signal analysis.
 18. Amethod as in claim 16 further comprising, subsequent to enabling thesecond approach for use in cardiac signal analysis and detecting two ormore cardiac cycles having intervals therebetween: analyzing intervalsbetween detected cardiac cycles; and determining whether plural suchintervals exceed one or more predefined thresholds and, if so, disablingthe second approach.
 19. A method as in claim 16 further comprising,subsequent to enabling the second approach for use in cardiac signalanalysis and detecting two or more cardiac cycles having intervalstherebetween, observing whether one or more amplitudes associated withone or more detected cardiac cycles fail to meet a minimum amplitudethreshold and, if so, disabling the second approach.
 20. A method as inclaim 16 wherein: the first approach uses a bandpass filtering in therange of 3 to 40 hertz; and the second approach uses a bandpassfiltering in the range of about 9 to 40 hertz.